Conventional surface protective layers and interlayer insulating layers for semiconductor devices typically include a polyimide resin which can have excellent heat resistance, electrical characteristics, mechanical characteristics, and the like. Recently, photosensitive polyimide precursor compositions which can be coated easily have been used as the polyimide resin. The photosensitive polyimide precursor composition is coated on a semiconductor device, patterned by ultraviolet (UV) rays, developed, and heat imidized, to easily provide a surface protective layer, an interlayer insulating layer, and the like. Accordingly, it is possible to significantly shorten the processing time compared with that of a conventional non-photosensitive polyimide precursor composition.
A photosensitive polyimide precursor composition can be a positive type in which an exposed part is dissolved by development or a negative type in which the exposed part is cured and maintained. It can be advantageous to use a positive type since it can be developed by a non-toxic alkali aqueous solution. A positive photosensitive polyimide precursor composition can include a polyimide precursor of polyamic acid, a photosensitive material of diazonaphtoquinone, and the like. However, the positive photosensitive polyimide precursor composition has a problem in that a desired pattern may not be obtained because the carboxylic acid of the polyamic acid is too highly soluble in an alkali.
Japanese Patent Laid-Open Publication No. H10-307393A is directed to a material including a phenolic hydroxyl group instead of carboxylic acid which is introduced by esterificating polyamidic acid with an alcohol compound having at least one hydroxyl group). This material, however, may be insufficiently developed, which can cause problems such as layer loss or resin delamination from the substrate.
Recently, a material in which a polybenzoxazole precursor is mixed with a diazonaphtoquinone compound has drawn attention (Japanese Patent Laid-open Publication No. S63-96162). When the polybenzoxazole precursor composition is actually used, however, layer loss of an unexposed part can be significantly increased, so it can be difficult to obtain a desirable pattern after the developing process. In order to improve this, if the molecular weight of the polybenzoxazole precursor is increased, the amount of layer loss of the unexposed part may be reduced. Development residue (scum) of the exposed part, however, can be generated, which can decrease resolution and increase development time on the exposed part.
It has been reported that the layer loss of the unexposed part can be suppressed by adding a certain phenol compound to a polybenzoxazole precursor composition (Japanese Patent Laid-Open Publication No. H9-302221 and Japanese Patent Laid-Open Publication No. 2000-292913). However, the effect of suppressing the layer loss of the unexposed part may be insufficient. Accordingly there is still a need to improve layer loss suppression and prevent development residue (scum) generation.
Furthermore, when this polyimide or polybenzoxazole precursor composition is prepared into a thermally cured film, the thermally cured film should have excellent mechanical properties such as tensile strength, and elongation, when it remains in a semiconductor device and acts as a surface protective layer. However, generally-used polyimide or polybenzoxazole precursors tend to have inappropriate mechanical properties, in particular, poor elongation, and also poor heat resistance.
In order to solve this problem, it has been reported that various additives can be added thereto or a precursor compound that is cross-linkable during the thermal curing can be used. However, although such additives or precursor compounds may improve mechanical properties, such as elongation, they may not provide desired optical characteristics such as sensitivity, resolution, and the like. Accordingly, there is still a need for materials and methods that can provide excellent mechanical properties without substantially deteriorating optical characteristics.